A memory system including a storage medium and a memory controller to control the storage medium is known. The memory system stores data instructed to be written from the host device, and transmits to the host device data read from the storage medium through an instruction from the host device. The memory system may be instructed to write particular data and instructed to read that particular to-be-written data before the write process into the storage medium is completed. Such data read process needs to be performed while satisfying various requirements imposed on the memory system.